Signaling system



March 6, 1951 D. slLvERMAN 2,544,569

SIGNALING SYSTEM Filed Dec. 17, 194e 2 sheets-sheet 1 fz [m] m 15 March 6, 1951 Filed Dec. 17, 1946 D. SILVERMAN SIGNALING SYSTEM 2 Sheets-Sheet 2 and the like.

the true signal.

Patented Mar. 6, 195i SIGNALING SYSTEM Daniel Silverman, Tulsa, Okla., assignor to Stanolind Oil and Gas Company, Tulsa, Okla., a corporation of Delaware Application December 17, 1,946, Serial No. 716,860

4 Claims.

This invention relates to signaling systems Vwhich employ the earth as a conductor of electric signals, and more particularly to signaling .systems for the transmission of signals to and from' apparatus within a well during the process of drilling.

' Systems for signaling through the earth are ,highly useful for many purposes, especially for geophysical prospecting, drilling Wells, and mam1 A.operations connected with the producing of oil and'gas; for example, such systems may be used to set ofi explosive charges, fire gun perforator, control valves, and' other apparatus below the earths surface, such as in Wells, mines, caves,

One very common use is in connection with logging wells in which data concerning events or the formations at the bottom of the Well are determined and reported without "an appreciable time delay to surface apparatus for indicating or recording.

In any signaling system, it is important that the signal, be free of noise or that the noise be eliminated in order that the signal is not distorted or destroyed. Noise is a term used herein to describe extraneous 'or foreign currents or potentials which are picked up by the receiving circuit of a signaling system and unless suppressed or ltered out, will be indicated and recorded, thus modifying and rendering erroneous In signaling systems such as the type contemplated by my invention, one

source of this noise that has-been recognized is the earth currentswhich flow in a horizontal path beneath the surface ofthe earth. These `are usually D. C. or very low frequency A. C. "currents of small magnitude.

There are various sources of these currents, one being that due to the electrolytic effect of ores, such as the Telluri'des.

Because of the presence of these earth currents, a signal receiving circuit, as for example, one comprising a pair of ground electrodes suitably connected to an amplifier and an indicator 'or recorder, will, in the absence of suitable compensating means, pick-up a small D. C. or low frequency A. C. potential between the electrodes. `Where the signal is a pulsating D. C. current, it

amplifier in the receiving circuit, these D. C.

potentials have been presumed to be ltered out by the amplifier and thus no other compensa- In signal- (Cl. Z55-1) -provide a method of transmitting signals and a of the noise entering the receiving circuit.

ning and when the rig is shut down. This is true even though the potential due to the earth 'currents was compensated for in a conventional :manner prior to the transmission of the signals.

I further observed that this discrepancy could be substantially reduced by stopping only the rotary table and the drill of the drilling rig permitting the pumps and engines to continue to run. As a result of these observations, I have concluded that there is another source of noise during drilling which must be taken into account.

I have discovered that the above discrepancy 'which occurred between the signals that were indicated and recorded in a Well logging system vwhile drilling and While not drilling is due to an increase, as well as a change in the character, I have further discovered that this additional noise component is due to the seismic-electric l,effect resulting from the mechanical vibrations transmitted through the earth from the equipment on the surface of the earth as Well as from fthe rotation of the drill in the earth. The existence of a seismic-electric effect, that is, the

,modulation of an electric current passing through the earth by a seismic disturbance, is

'a well-known phenomena that has been the basis for seismic-electric methods of prospecting. The effect is the result of a change in the resistance or impedance of the earths formation due to mechanical vibrations or seismic Waves passing through these formations.

It is the object of this invention, therefore, to

signaling system employing the earth as a conductor of electric signals for use in a portion or region of the earth that is being subjected to seismic disturbances with a higher degree of accuracy than has heretofore been possible. It

'in connection with Wells, caves, and the like,

whereby noise, which might otherwise be retem which will'make a log While drilling is in Y progress substantially identicall with the; log` that would be obtained if the drilling', were stopped. These and further objects and advantages of my invention will be apparent 1`Qlfl. the following description of my invention as preferably applied in a type of signaling system which employs the earth as a conductor-of elec,- tric signals.

The preferred application is in a Well logging-n while-drilling system similar to that describedinl detail in Silverman et al. U. S'. Patent 233541,88?? and modified in accordance with the present;in;- vention. In this system some characteristic of .the formation adjacent, the well near the drill oit.. is. detected. by an electrical apparatus, such an. insulated, electrode. surrounded by. an. elec.- trical iield. When. an. electrical.v characteristic, of the formation changes, as for example, the7 13e,- Slvty Olt leaotallce, tlleeld undergoesa correspfmdiiig variatlon. which. is transmitted. to the surface for detection and.: recording, Transmis.- Slohtalses place over. a oath including, the earth and the drillA pipe. Which, latter. serves as. areturn circuit. The detectmg. and recordinecircoit located on the surface. of.V the earth. includes at least two grounded o r surface electrodes:one Qf which. may bethe drill nipaeleotrically. connected to a suitable amplifier, which in turnis connected to a.. Suitable indicator and recorder. rIlle.. recorder maires a. chart of the signals. received as afuhction of time or depth- As pointed out above, there. exists between the surface electrodes. a small potential.. having both D. C- ahd Al C. components which is cluel tothe earth currents. A seismic Wave disturbance set up in the earth in the vicinity of theseieleotlcdes would, as a. result. of the. seismic-electric effect, cause a modulation. of; this. potentialac.- cordins to the amplitude and; frequency of. the seismic wave. In. well loeeinofwhile-drillinasys,- tems previously kho-wh to niethemodulated rotential. Would. be. picked-up and; erroneously. ih.- fiueiice the. reception and. recording, of. thev true Signal. FilteringA devices. would. not. be, suitable since. the modulated earth currentmay have com.- ponents o f the same, frequency asthe signal,... 'llhis is particularly truev where. the. sional; current.Av is of' aV low frequency, which is` preferable for trans.,- mission. tok great. depths below. the, surface,Z for example, frequencies of 10 C. E'. S.or1css.

I n accordance With. my invention, thereforeil provide in my improved Wellloggingewhileadrilling system a, sourceA of; compeIlSttlki/ng electrical potential having an electrical characteristic which variesin response toa seismic disturhance inthe same manner as someone orv more components of the earth. currents vary in. respons e to the same disturbancev and this; varying potentialis utilized inoppositionto,v thevarying potential due to the earth currents which. may otherwise influence. the indicated signal sotasto cancel out the same, and hence reduce thenpise.

In one embodiment of, my wellvv loggingisystem L may employ 's uitable.mea ns, as. for example a seismometer, for. converting seismic wavesinto a varying electrical potential having-v electrical characteristics corresponding to those; o fI the modulated earth currents- The output, of theA seismometer is introduced into the receiving circuit of my well logging system in opposition the signal current. In this embodiment, the signal current will comprise the signals transmitted by the logging electrode plus noise due to the earth currents modulated as a result of the seismic-electric effect. Now, since the compensating potential which I introduce into. or impress on the, receiving, circuit is` one having; electric characteristics indicative of the seismic waves and hence substantially identical to the varying potential of the modulated earth currents, the potentials will cancel out and my recording mechani-smV willrecord orindicate substant'ally the true signal. A modification of this embodiment of4 my invention.` comprises introducing into the receiving circuity a compensating potential having a frequency cor-responding to the main comparlent; of the seismic waves, which I have found Y by observation is generated by the rotary table and the drilL This, latter modihcation accomplishes. at. least. a. substantial reduction, in., noise level and thusr permits. the. recording or signals which are far. more., accurate. than. have heretofore. been possible. Because of. the, complexity of the seismic waves which are introducedby the mechanical. vibrations. of. the. various pieces of equipment, taking part. in.V the.. drilling operation, no. one. embodiment. may effectively eliminate, all the. noise.Y and. consequently. I, contemplate that it may be advantageoustousetwo orv moremethodls combination.

invention. will.; be better understood when reference. is. made. to. the attached. drawings 0fv preferred embodiments of, well loosing systems. formino a part. hereoh, wherein like numerals have. the. saine. significance... In. these. drawings! Figure. 1.A is a4 verticali cross. sectional. view through. a portion of the, earth. nenstratied.` by a Well, showing diagrammatically all embodiment' of. my well logging-While:drilling, systemwherein the. outnutofi a. selsinometer is utilized. to onpose the potential receivedby detecting electrodes whereby the. influence. of. modulo.ted` earth. currents issubstantiallv nulliiiedg Figure Zlis, similar. to. Figure 1. Whereinastrain ease replacesthe. seismorneten.

Figure. 3.y is still a: further. embodiment'. similar to, Figure L wherein. the potential; introduced`V into the. receiving. circuit. is, that., received, by a. pair of eround;el;ectrocles and.. wherein. preferably the electrodes are. eouidistant fromeachot thepi'ck.- up, electrodes.. of. the receiving. circuit., and hence receive only. the. modulated. earth. currents..

Figure. 3o..,isa diagrammatic plan view. showina. the electrode-arrangement.oithe. embodiment in FigureV 3.

Eieure lY is` still another embodimentsimilar. to Figure 1 wherein the compensating potentialL in;- troduced into. thel receiving" circuit, is, generated atv a frequency prop,or...ti.i.ina1v tothe R.YA P.. of thewdrill..

Referring particularly now, te Figure, l, in, the drawings extending within. a.` Well I in. the. earth 2 isa rotary drill pipe. 3,v including,- on. the.. end thereof.Y a. drill loitxl.A 'Ilhefdrill pipe issupported by a. suitable drilling, derrick, not-shownonfthe surface, of. the earth, andT ist. rotatedL by.. a.` rotary table. 5, which ini turritisf driven through. a. pinion tbv.' a.i suitable power sourcenotshown., Mgmvention, while. shown. withl reference to, rotary drilling, is alsoanplicableto `cable drilling,-

CoupledV tothe. drill. pipe, at ai, point. adjacenty the drill bitV through a.. suitabletransxnitting elec.- trede, 1, is l asignalgenerator,V 8.3 servingas asource of electrical signals within the earth. Signals transmitted by the transmitting electrode are preferably low frequency alternating currents,

e. g., 10 C. P. S. or below, although frequencies in the audio and radio range may be used, having varying electrical characteristics, such as frequency or amplitude, indicative of the electrical 'properties of the formations in the immediate vicinity of the electrode. These frequency or amplitude modulated currents flow through the earth, as represented by paths 9, and they are eventually detected at the surface of the earth by a receiving circuit. This circuit includes at least a pair of surface electrodes II) and I I. Electrode II is preferably the drill pipe 3 as shown. The surface or ground electrode III may benonpolarizing or otherwise. The surface electrodes I and II are connected to an amplifier I2 where the signal is amplified. The output of the amplifier passes to a recorder I3, through a coupling transformer I4 wherein a chart is made showing the variations in the signal as a function of time or in some cases of the depth of the transmitting electrode in a manner well-known in the art.

When the signal generator is silent, a potential will be found to exist between the surface electrodes Ill and II which can be indicated by a voltmeter I5 in the conductor I6. This potential is'due to the earth currents which, as pointed out above, will comprise both D. C. and low frequency A. C. components. Insofar as the D.'C. components are concerned they would not be amplified and it has heretofore been assumed that no error would be introduced by their presence. The same is true even as to the low frequency components, which are generally less than 1 C. P. S. where the amplier is the conventional audio or radio frequency type. When, however, lthe drilling apparatus is operating, the voltmeter I5 will show a pulsating potential between the electrode I0 and II which will be amplified and thus influence the recorded signal. This pulsating potential is the result of the seismic-electric effect due to the mechanical vibrations introduced into the earth by the various apparatus comprising the drilling rig, including specifically the rotary table and the drill.

To eliminate or reduce this source of noise or at least the D. C. component thereof, I employ a seismometer II, or equivalent vibration pickup, which may be any of the conventional types which are used in seismic surveying, preferably positioned on the ground between the drill and the vground electrode, the output of which is fed to an amplier I8 having suitable phase shifting means. This output current may be a pulsating D. C. current or modulated A. C. having electrical characteristics indicative of the seismic waves to which the seismometer responds. I then impress the amplified output of the seismometer and the output of amplifier I2 of the receiving circuit on the coupling transformer I4. The output current of the seismometer is set in opposition to the signal current by a phase-shifting means in the amplifier I8 and will tend to cancel out that component of the potential picked up by the surface electrodes having similar electrical characteristics due to the seismic-electric effect.

In order to adjust the magnitude to which the output of the seismometer is to be amplified to match the magnitude of the noise and thus to avoid over-correcting, I may, for example, have an oscillograph I9 connected across the secondary of my coupling transformer Ul and adjust the amplier I8 until I obtain a substantially clear,

sharply defined wave form on the oscillograph of minimum amplitude. This will indicate the point at which substantially all the noise has been canceled by the opposing output current of the seismometer and at which substantially the pure signal current is passed to the recorder. Once this setting of the amplifier I8 has been made, the signaling system will operate accurately so long as there is no substantial change in the nature of the seismic disturbances produced by the drilling equipment. It will, of course, be apparent that where the signal generator within the well can be momentarily stopped that it will not be necessary to utilize the oscillograph to adjust properly the amplifier I8. In this case, it is only necessary to adjust the amplifier to give a minimum reading on the recorder, which minimum reading will be the zero point on the graph recording the logging signals. In most of the conventional logging systems, the signal generator, once placed within a well, operates automatically and, therefore, it is not possible to show on the recorder solely the noise in the receiving circuit; however, a time schedule may be set up whereby the generator would shut periodically.

In the embodiment of Figure 2, in place of the conventional seismometer, I discovered that since the noise will have a wave form characteristic of mechanical vibrations, I may utilize a strain gage 20 as my pick-up for the seismic waves. The strain gage includes an extensible metallic member which becomes a variable resistance upon elongation and contraction due to mechanical vibration. By placing the gage in a position where the mechanical vibrations of the drilling equipment can be transmitted to the gage causing it to vibrate with the same periodicity and by passing a current through it and a series resistance, I obtain another source of potential across the resistance having the electrical characteristics of frequency and wave form similar to the noise due to the seismic-electric effect.

Although the strain gage, as the seismometer, may be secured to or mounted on one of the major sources of the vibration, such as the derrick support for the drill, in the floor of the drill derrick, or in some other structural part of the drilling mechanism, possibly a part of the rotary table, I prefer to bury it in a shallow hole in the surface of the earth and position it in a radial alignment with the direction of the seismic waves, preferably between the surface electrodes, in order that it may be more responsive to the seismic waves.

The output of the strain gage circuit, which circuit includes a battery 2I and a resistance 22 in series with the gage element, is fed to the amplifier and phase shifter 23, preferably through a blocking condenser 26. The output of the amplier is then impressed on the coupling transformer I4 for the recorder I3 and the magnitude of the output adjusted as in the case of Figure l to give a clear wave of minimum value. Incidentally, this method of adjusting magnitude is applicable to any of the embodiments described herein.

In Figures 3 and 3a, I have shown an embodiment of my invention wherein my opposing or correction current is the noise due to the modulation of the earth currents which I pick up to the exclusion of the signaling current. These modulated earth currents I then amplify and introduce into my receiving circuit in opposition to the signals beingreceived. I accomplish this by having a second receiver station comprising a pair of assesses 'groundedlelectrodes 25 and 2.6 which Ispace .equi-y -distant from the drill pipe 2 and preferably from the grounded electrode l0. A varying potential difference will occur between these two electrodes due to the seismicfelectric effect on the earth currents, as is welleknown in seismiceelectricsurveying, whichl amplify inan amplner and phase shifter 27, the output of which is then fed to .the coupling transformer l. By arrangingmy elec: trodes and v26 in the preferred manner de.- scribed above, they both lie on an equifpotential line .of the eldof the signaling electrode and con sequently do not receive vany component ,of the signaling current. This embodiment requires very simple apparatus vand gives very satisfactory z,

results.

In Figure 4, I have shown an apparatus, wherein thecurrent or potential that I introduce into my receiving .circuit to cancel :the noise component due to the seismic-electric effect, is not indicative of the composite seismic disturbance lout of a major component of such disturbance which, as indicated above, I have observed in the .case of my example to be the rotary table and the drill. Therefore, in this embodiment I generate, by means vof a generator 36 connected through shaft 3l and gear Sla tothe rotary table 5, an alternating .current having a frequency which is proportional to the jR. P. M. of the vrotary table and .hence proportional to the component of seismic disturbance in the earth due to the rotary table .and drill. This alternating current from generator 3i] is passed through conductors 33 and 36 to a phase-shifting ,means of any conventional design and thence through conductors 36 and 3l ampleof a mixing circuit which l' may use comprises a pair of ytriodes 4I and d2.

The .output from amplifier l2 is fed to the grid d3 of tube li i,

vwhile that from ,the generator is fed to the' grid 44 of tube 4,2. Y The plates 45 and 46 of the two tubes are connected in parallel through :the block- Aing .condenser 39 Vto :the .amplifier .40. .The plate voltage vfor the triodes is supplied by a battery lll vconnected intofthemixing circuit through a plate resistor i8, The lament .current is suppliedby another battery not shown.

lThough I have described several embodiments of vmy invention las applied to a well .logging-whiledrilling signaling system, it will be readily apparent `to those skilled inthe art that with little modification my invention may be .appliedto other signaling systems whether or not the signal is transmitted from within the'well, as in well logging, or from the surface of the earth to a receiving station Within the well. Furthermore, it

Willbe applicable whether the signal current is preferably a low frequency alternating current, a D. C. or high frequency alternating current. My invention is Yapplicable to any signaling-system wherein the noise is received along with the desired signal bythe receiving system and wherein at least one component of that noise is due to the .seismic disturbances in the earth. Other embodiments and modifications will be apparent to :ances wherein signals are sent between a remote point beneath the surface of the earth and ya .point on the surface along a path including the earth as a conductor, and wherein the seismic disturbances modulate .earth currents near the surface uf the earth due t0 the Seismiofelectric effect, which modulated earth currents adversely influence detection of the signals, the combi,- nation 0f a primary source 0f potential, a transvniitting circuit including said primary source uf potential fior transmitting electrical signals through .the earth. means vCoupled to the .earth for detecting a varying electrical potential in the earth which is derived from said signals and lsaid modulated earth currents, an electrical gen; erator providing a second potential independent of said varying electrical potential and having a frequency substantially equal to at least one ycomponent of said modulated earth currents, and means for impressing said second potential upon the circuit of said detecting means in such time relationship that said second potential lis in elec;- trical opposition to said vcomponent of said modulated earth currents of the same frequency.

2; In a signaling system which employs the earth as a conductor of electrical signals, :for use in a portion of the earth being subjected-.to

Vseismic disturbances, means for introducing electrical signals into the earth, means coupled to the earth `for detecting a varying electrical volt;- age in the earth, said electrical voltage being d erived from said signals and yfromelectrical disturbances including seismic-electric effects, means independent of said detecting means kfor supplying a potential having electrical characteristics indicative of said seismic disturbances, and means for impressing said potential on said .detecting mean in such time relationship with Athe varying electrical voltage received that said .poftential is in electrical opposition to that portion of said varying electrical voltage which is derived from said seismic disturbances.'

3. In a signaling system for use in a vportion of the earth beingsubjected to seismic disturbfances, means for introducing electrical signals `into'the earth, means coupled to the earth Vfor Adetecting a varyingelectrical voltage in the earth,

saidvarying electrical voltage being derived from said ,signals and from electrical disturbances including seismic-electric effects due to saidscisrnic isturbances, an electric generator independent of ,said detecting means andhavingan output o fa frequency substantially equal to at least `one .component yof the seismic waves in `the Aearth .dueto the presence of said seismic disturbances, and circuit means for combining the output of ,said generator and the output of said voltage-detectling means, with the generator output being in electrical .opposition to the component of said electrical `voltage due to said lseismic disturbances.

4. In a well signalingsystem for use in a well during rotary drilling, means ior introducing electrical signals into the portion of the earthsubjected to seismic disturbances by said drilling, means coupled to the earth for receiving .said electrical signals after transmission through the earth, said receiving means being sensitiveV l.also to electrical disturbances in theearth due to the seismic-electric effect of said drilling, an electric generator independent of said 'receiving means and coupled to the drilling device for generating a potential having a frequency proportional to the speed of rotation of the drill, and an electrical circuit .coupled to said signal-receiving means and to said generator for combining the outputs of Said signal-receiving means and of said electric generator in such time and phase relationship that said generator output is in electrical opposition to at least one component of said electrical disturbances received by said signal-receiving means.

DANIEL SILVERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS Name Date Jakosky Apr. 11, 1939 Owen Sept. 17, 1940 Owen Oct. 1, 1940 Silverman et al. Aug. 1, 1944 Douglas Dec. 12, 1944 Steinhoff May 22, 1945 Ennis Mar. 26, 1946 Pearson et al. June 4, 1946 Guyod Sept. 30, 1947 Wolf Nov. 25, 1947 Johnson Mar. 25, 1948 Clewell Nov. 30, 1948 Gilmore Dec. 14, 1948 

